The Long Term Evolution (LTE) system has been standardized in the 3rd Generation Partnership Project (3GPP) as the next generation global standard for radio communication systems. The LTE system is constituted by a radio communication terminal UE (User Equipment), a radio communication base station eNB (evolved Node B), and an EPC (Evolved Packet Core) which is the core network of an IP (Internet Protocol) base. In the present disclosure, a radio communication base station is abbreviated as a “base station” as appropriate, and a radio communication terminal (mobile terminal) is abbreviated as a “terminal” as appropriate.
Handovers in E-UTRAN (Evolved Universal Terrestrial Radio Access Network), i.e. the LTE system, have also been standardized in 3GPP (for example, see Non-patent Literature 1 and Non-patent Literature 2). The following schematically describes a handover in the LTE system as prescribed in Non-patent Literature 1 and Non-patent Literature 2.
FIG. 7 is a sequence diagram illustrating a handover within the MME (Mobility Management Equipment)/S-GW (Serving-Gateway) described in Non-patent Literature 1. In the LTE system, prior to the performance of a handover, a terminal (UE) makes a variety of measurements on other base stations neighboring the Serving Cell (Source eNB in FIG. 7), which is the cell currently serving the terminal. The terminal performs these measurements on base stations neighboring the Serving Cell based on the Measurement Configuration reported by the Serving Cell (#1 “Measurement Control” in FIG. 7). The Measurement Configuration is transmitted to the terminal by a message called an RRC Connection Reconfiguration. The measurements performed here on the base station include, for example, measurement of RSPP (Reference Signal Received Power: signal strength), RSRQ (Reference Signal Received Quality: signal quality), base station ID, and the like.
The results of measurements are reported to the Serving Cell as a Measurement Report (#2 in FIG. 7), and based on reported measurement results, the Serving Cell determines a base station to be the target of the handover performed by the terminal (Target eNB).
When a terminal performs a handover between base stations in this way, the terminal can be made not to perform the above-described measurements for a portion of the other base stations neighboring the Serving Cell. This approach may be implemented by registering, in the Measurement Configuration reported by the Serving Cell, specific base stations among the base stations neighboring the serving cell as being excluded from the above-described measurements. Thus registering a specific base station as being excluded from measurements normally made before performance of a handover is referred to below as “placing a base station on a blacklist”.
This blacklist is included in a parameter called Measurement Object in the Measurement Configuration. In greater detail, when the carrier frequency of a specific base station is included in the blacklist, that base station is blacklisted. In Non-patent Literature 2, the parameters in the Measurement Configuration, including the Measurement Object, are prescribed along with other details.
There is no clear prescription in the 3GPP Standard regarding the occasion or method for placing a base station on a blacklist as described above. Accordingly, it is assumed that the occasion and method for placement on such a blacklist will be determined by agreement between the carrier and the vendor.
By thus placing specific base stations on a blacklist, specific base stations can be excluded from a variety of measurements. Accordingly, by adopting this blacklist, it has been proposed to reduce power consumption by, for example, preventing frequent measurements for Measurement Reports (for example, see Patent Literature 1). Patent Literature 1 also proposes implementing a blacklist to reduce overhead for receiving system information from a base station.
For example, when an area within a certain macrocell is covered by a plurality of microcells, and a terminal is moving at high speed through such an area on a train, car, or the like, then it is assumed that measurements will occur frequently not only for the macrocell but also for the microcells. In this example, since the terminal is moving at high speed, frequent handovers between microcells are of little value and are not desirable. Therefore, by placing base stations forming microcells on a blacklist, for example, it is possible to make only the base stations forming the macrocell the target base stations for a handover. With this approach, the processing load on the terminal can be reduced by preventing the terminal from performing frequent measurements, and power consumption can also be reduced.